This invention relates to the preparation of heavy denier, polyamide monofils having both high straight and high loop tensile properties.
Such filaments and their utility as reinforcements, e.g., in tires, have been described in U.S. Pat. No. 3,650,884 to Hansen. To insure cooling below the glass transition temperature and solidification before reaching the draw zone, the heavy denier monofil of Hansen is first advanced through an air gap and a water quenching bath. In the practice of those steps, conditions are carefully controlled but birefringence and transcrystalline orientation are nevertheless developed in a skin layer. That layer presents difficulties in the achievement of the desired extent of orientation in two coupled, radiantly heated, draw stages. The skin layer is deoriented and loop tenacity is improved by advancing the drawn filament through a zone of saturated or wet steam. Although operable, the existing process has shortcomings such as criticalities in the quenching steps, limitations on the extent of orientation in the draw zone and high contact time in the postdraw steaming step.